Publications by Author: Bertran, Ramon

J. Leng, A. Buyuktosunoglu, R. Bertran, P. Bose, and V. J. Reddi, “Asymmetric Resilience for Accelerator-Rich Systems,” Computer Architecture Letters, 2019.Abstract
Accelerators are becoming popular owing to their exceptional performance and power-efficiency. However, researchers are yet to pay close attention to their reliability---a key challenge as technology scaling makes building reliable systems challenging. A straightforward solution to make accelerators reliable is to design the accelerator from the ground-up to be reliable by itself. However, such a myopic view of the system, where each accelerator is designed in isolation, is unsustainable as the number of integrated accelerators continues to rise in SoCs. To address this challenge, we propose a paradigm called "asymmetric resilience'' that avoids accelerator-specific reliability design. Instead, its core principle is to develop the reliable heterogeneous system around the CPU architecture. We explain the implications of architecting such a system and the modifications needed in a heterogeneous system to adopt such an approach. As an example, we demonstrate how to use asymmetric resilience to handle GPU execution errors using the CPU with minimal overhead. The general principles can be extended to include other accelerators.
J. Leng, A. Buyuktosunoglu, R. Bertran, P. Bose, and V. J. Reddi, Asymmetric Resilience: Rethinking Reliability for Accelerator-Rich Systems. IBM, 2018.Abstract
We have already entered the heterogeneous computing era when computing systems harness computational horsepower from not only general purpose CPUs but also other processors such as graphics processing unit (GPU) and hardware accelerators. Performance, power-efficiency, and reliability are three most critical aspects of processors, and there usually exists a tradeoff among them. Accelerators are heavily optimized for performance and power-efficiency rather than reliability. However, it is equally important to ensure overall reliability while introducing accelerators to computing systems. In this paper, we focus on optimizing accelerator’s reliability without adopting the “whac-a-mole” paradigm which develops accelerator-specific reliability optimization. Instead, we advocate maintaining the reliability at the system level, and propose the design paradigm called “asymmetric resilience,” whose principle is to develop the reliable heterogeneous system centering around the CPU architecture. This generic design paradigm eases accelerators away from reliability optimization. We present the design principles and practices for the heterogeneous system that adopt such design paradigm. Following the principles of asymmetric resilience, we demonstrate how to use CPU architecture to handle GPU execution errors, which allows GPU focus on typical case operation for better energy efficiency. We explore the design space and show that the average overhead is only 1% for error-free execution and the overhead increases linearly with error probability.
J. Leng, A. Buyuktosunoglu, R. Bertran, P. Bose, and V. J. Reddi, “Safe Limits on Voltage Reduction Efficiency in GPUs: A Direct Measurement Approach,” in Microarchitecture (MICRO), 2015 48th Annual IEEE/ACM International Symposium on, 2015, pp. 294–307. Publisher's VersionAbstract

Energy eciency of GPU architectures has emerged as an important aspect of computer system design. In this paper, we explore the energy benefits of reducing the GPU chip’s voltage to the safe limit, i.e. Vmin point. We perform such a study on several commercial o↵- the-shelf GPU cards. We find that there exists about 20% voltage guardband on those GPUs spanning two architectural generations, which, if “eliminated” completely, can result in up to 25% energy savings on one of the studied GPU cards. The exact improvement magnitude depends on the program’s available guardband, because our measurement results unveil a program dependent Vmin behavior across the studied programs. We make fundamental observations about the programdependent Vmin behavior. We experimentally determine that the voltage noise has a larger impact on Vmin compared to the process and temperature variation, and the activities during the kernel execution cause large voltage droops. From these findings, we show how to use a kernel’s microarchitectural performance counters to predict its Vmin value accurately. The average and maximum prediction errors are 0.5% and 3%, respectively. The accurate Vmin prediction opens up new possibilities of a cross-layer dynamic guardbanding scheme for GPUs, in which software predicts and manages the voltage guardband, while the functional correctness is ensured by a hardware safety net mechanism.